Our laboratory has been concerned with mammalian genetics, development, and cell biology. We have been particularly concerned with parasexuality in somatic cell populations maintained in tissue culture, and the use of parasexual events for the development of new systems of genetic analysis. We have made use of man/mouse somatic cell hybrids in order to establish mammalian gene maps --and particularly, a human gene map. Recently, we are pursuing studies on gene transfer in mammalian cells. Such systems are useful in high resolution gene purification, and in gaining information relating to mechanisms of gene regulation. These mammalian cell/gene transfer systems have shown that small fragments of donor chromosomes and purified DNA can reside in recipient cells as unintegrated or as integrated replicating transgenomes. It is also clear that they can exist in a broad range of sizes. We believe the mammalian transformation systems have potential for cloning of mammalian genes, and further as means of testing their genetic function under a variety of controlled, experimental conditions.